Play Catch Achievement in Doom 3: BFG Edition
Kill 20 enemies with projectiles launched from the Grabber in RoE
How to unlock Play Catch
The Grabber (also known as the IPL) is a weapon very similar to the Gravity Gun from Half-Life 2. It can grab objects and toss them, and can even be used as a weapon in itself. The Grabber will be obtained right near the start of the game from a dying Marine. You will need to toss objects at 20 enemies and kill them with said tossed object.
On a related note, the Grabber is extremely useful for Forgotten Ones (fiery flying skulls) as it is an instant kill.